Electrode structure for electron



United States Patent 2,901,657 ELECTRODE STRUCTURE FOR ELECTRON WilliamR'. Stuart, Millbrae, .Califi, assignor to Eitel- McCullough", Inc., SanBruuo,.Calif., a corporation of California Application July.30,:1-956,SeriaLNo. 600,807

4 Claims. (Cl; 313-257)" This invention relates generally to electrontubes.

Prior art electron tubes have been subject to the disadvantages thatshock' and vibration causes movement of the grid elements and cathode.This often results in shortingbetween the control grid and the cathodeand between grid elements; Undesired changes in tube characteristicsalso result.

It is a general object of the present'invention to provide an improvedelectron tube structure.

It is another object of the present invention to provide means forpreventing movement of elements of an electron tube.

It' is another object of the present invention to provide means forpreventing relative movement between the gridand cathode elements.

It is afurther objectof'thisinvention to provide an improved electrontube in which the grid and filament are held coaxial by means of aninsulating disk.

It is a further object of the present invention to provide an electrontube having a control grid which serves to support an insulating spacerwhich accommodates the cathode post to prevent relative movement betweenthe cathode and grid.

It is another object of the invention to provide an im proved electrodestructure of the type formed from a plurality of wire bars wherein saidwire bars serve to clamp into the electrode structure an insulatingspacer member.

The invention possesses other objects and features of advantage, some ofwhich with the foregoing will be set forth in the following descriptionof the invention. It is to be understood that the invention is not to belimited to the particular disclosure of a species as other embodimentsmay be adopted within the spirit of the invention and the scope of theclaims.

Referring to the drawings:

Figure 1 is an elevational view partly in section of an electron tubeembodying my invention;

Figure 2 is an enlarged sectional view taken along the line 2-2 ofFigure 1; and

Figure 3 is an enlarged elevational view showing the control gridstructure and insulating disk.

Referring to the drawings, the tube comprises an envelope of glass orother suitable material with exhaust tubulation 12 arranged at thecenter of the lower portion thereof.

The multi-gn'd tube illustrated is a tetrode having four electrodesindicated generally at 11, including an anode 13, screen grid 14,control grid 16 and cathode 17. The electrodes are concentric about theaxis of the tube.

The anode 13 is tubular in form, preferably cylindrical. It is open atthe bottom and preferably closed at the top by means of a cap 18suitably attached thereto. The cap serves to protect the upper end ofthe envelope against bombardment and also functions as part of themounting for the anode. The anode is mounted on a lead-in conductor 19which is sealed to and supported 'ice 1 which project upwardly throughthe'lower portion-22 of the envelope. The cathode-17 may be any suitabletype-of construction, but'preferably comprises a helical filamentofthoriated tungsten wire secured at the topto the cathode post 23 andatthe bottom to the bracket 24. The bracket and post are-attached to a.pair of the leads whichextend' through the lower portion of theenvelope.

Thecontrol grid 16 is preferably-of cage-type construction comprisinglongitudinal or vertical wire bars 26 reinforced by horizontal wirerings 27. The longitudinal grid elements terminate in a cup-shaped basering 28 to which they are attached as by spot welding. The gridprojectsinto the anode alongthe cathode and is sup ported by the controlgrid leads-which'extend through the lower envelope portion 22..

Wound into the topof=-the longitudinal control grid" wires 26 is aninsulating spacer disk '31 having a: hole 32 which accommodates with aclose fit the upper portion 33 of the central cathode post 23.Thepreferred'rnaterial for disk 31 is ceramic because of its mechanicalstrength and ability to withstand high temperature. 'As shown inFigures2 and 3, eight of thelongitudinal wires 26 are accommodated in notches34- and' formfour transverse portions 35 which extend chordally acrossthetop of the disk. The disk is held between these upper transverseportions 35 and the lower transverse portions 36. Thus, when the tube issubjected to vibration or shock, the cathode is held coaxial to thecontrol grid, and filament wires 37 are maintained in their spacedposition with respect to the grid structure 16.

A convenient method for forming the grid with the insulating spacer diskis to wind on a rod-like mandrel the first set of longitudinal bars 26;that is, the eight bars having the four transverse connecting portions36. The disk 31 is then placed against the transverse portions 36 whichit will be understood pass over one end of the mandrel. Finally the nexteight grid bars are wound on the mandrel with their transverse portions35 passing tightly over the disk 31, so that the disk is firmly clampedbetween the transverse portions of the two sets of grid bars. A sixteenbar grid has been disclosed as being desirable but a diiferent number ofbars can of course be used.

The screen grid 14 is also of cage-type construction comprisinglongitudinal bars 41 reinforced by transverse rings 42. The gridelements terminate in a cup-shaped base ring 43. The base ring 43 ismounted on a metallic shield 44 which is suitably secured to leads 45.

The shield 44 extends transversely of the electrodes and issubstantially coextensively with the cross sectional area of theenvelope. It is preferably cup-shaped and has its peripheral edges closeto the inner surface of the envelope. This arrangement shields theconductors in the lower part of the tube from the anode.

The base of the tube preferably comprises a metallic ring 47 suitablysecured to the envelope, as, for example, by cementing, and whichcarries an insulating disk 46 to which the prongs 48 are attached. Theseprongs are coaxially aligned with the leads extending into the en velopeand are hollow to receive the lead extensions.

As described, the insulating disk is interwound in the top of thecontrol grid and disposed to register with the upper portion of thecathode post. However, a disk of the character described may beinterwound into any one of the other elements and suitably engaged withthe post or another element of the tube to prevent movement of theassociated parts. Accordingly, one of the main features of the inventionrelates to the arrangement whereby an insulating spacer disk 31 is woundinto a cage-type electrode. In this manner the insulator is firmlyassociated with the electrode so that when the insulator is placed incontact with another element of the tube, for example, the cathode rodin the embodiment disclosed in Figure 1, then the electrode is heldrigidly spaced from such other tube element. A desirable feature of thedisclosed method of supporting the insulating disk is that the electrodeis wound directly around the disk, thus avoiding any extra procedure forattaching the disk to the electrode, such as by brazing.

An electron tube was constructed with an insulating disk which held thecathode and control grid elements coaxial. The tube was subjected toapproximately 60' Gs of acceleration and operated satisfactorily.Similar tubes, without spacing disks shorted out and became inoperativein the neighborhood of 27 Gs of acceleration.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. An electron tube grid comprising a plurality of U-shaped Wire barshaving the legs thereof extending longitudinally of the grid to definecircumferentially spaced elements of a cylinder, a supporting base towhich said wires are secured at one end of the cylinder, and at theother end of the cylinder an insulating member having opposite facesthereof extending transversely of the cylinder, the base of certain ofsaid Wire bars extending across and engaging one face of said member,and the base of others of said wire bars extending across and engagingthe other face of said member, whereby said member is gripped betweensaid wire bars to form with the latter a rigid structure.

2. A grid as claimed in claim 1, in which said insulating member isperipherally grooved to receive certain of said Wire bars to preventcircumferential displacement thereof. a

3. An electron tube having a plurality of electrodes including a grid,said grid comprising a plurality of U-shaped wire bars having the legsthereof extending longitudinally of the grid to define circumferentiallyspaced elements of a cylinder, a supporting base to which said wires aresecured at one end of the cylinder, and at the other end of the cylinderan insulating disk extending transversely of the cylinder, the bases ofcertain of said wire bars extending across and engaging one face of saiddisk, and the bases of others of said wire bars extending across andengaging the other face of said disk, whereby said disk is grippedbetween said wire bars to form with the latter a rigid structure, and asecond electrode having a support engaging said disk to prevent relativelateral displacement thereof.

4. An electron tube as claimed in claim 3, in which said secondelectrode is a cathode, and said support is a rod extendinglongitudinally of said grid structure, said disk being apertured toreceive said rod.

References Cited in the file of this patent UNITED STATES PATENTSSimpson Oct. 9, 1951

